140 ROBERT TRACY JACKSON ON ECHINI. 



chusetts. This is of interest as the most southern locality represented. The specimens were 

 dredged in shallow water under open ocean conditions. In this series there are many small us 

 well as large specimens, so for comparison they are divided into two sets. The first from the 

 Truro locality, is composed of small specimens, 20 to 30 mm. in diameter. In this set (1,100 

 specimens) only 0.3 % have ocular I only insert. This is a smaller proportion than in the 

 larger series, doubtless a mere coincidence, but it shows that the specimens are fully developed 

 in regard to this character, whereas the 20 to 30 mm. series from Dumpling Islands (see table, 

 p. 142) is less developed in this character than larger individuals of that locality. The Truro 

 specimens of this series have 96 % with oculars I, V insert, a higher percent than the larger. 

 On the other hand, of the progressive variant I, V, IV insert, there are only 2.9 % instead of 

 4.3 % as in the larger series, indicating that this character develops in later growth. Of aber- 

 rant variants there is 1 %, consisting of five specimens with oculars I, IV and eight with I, V, II 

 insert. The second set from the Truro locality consists of larger specimens ranging from 30 

 to 60 mm. in diameter. In this series (1,700 specimens) 0.6 % have ocular I only insert, 94 % 

 have I, V, and 4.3 % are progressive variants with I, V, IV insert. One specimen, 0.06 %, has 

 I, V, IV, II insert. The aberrant variants are 1 %, of which there are six specimens with 

 oculars I, IV insert; two with V, IV; two with V, II; and ten with I, V, II insert. This series 

 has gained in I, V, IV insert at the expense of the I, V as compared with the smaller series. It 

 is of interest as it is marked by the least number of arrested variants and the greatest number 

 of progressive variants of any locality on the New England coast (table, p. 143). 



A series of 200 specimens from Labrador is interesting as representing a northern locality. 

 Arrested variants with ocular I only insert are rather frequent, 2.5 %. The specimens are so 

 small that it is possible that some of them are developing individuals and a series of larger 

 specimens might show fewer arrested variants. The same statement also applies to the next 

 series considered. The Labrador lot has 87.5 % with ocular I, V insert, and 7.5 % of progres- 

 sive variants with oculars I, V, IV insert. Aberrants are 2 %, being three specimens with 

 oculars I, IV, and one with I, V, II insert. 



Through the kindness of Dr. Mortensen I have a series of 35 specimens from Iceland and 

 the Faroe Islands. These both show practically identical characters, so are treated together. 

 They are of special interest as being the most northern locality represented and also as showing 

 the most progressive character seen in the species. The specimens are medium sized, a few 

 are small. Of arrested variants 11 % have ocular I only insert, a strikingly high percentage 

 for the species and especially as the progressive variants are frequent. Only 60 % have oculars 

 I, V insert, almost the lowest percentage known in the species, and 20 % have as progressive 

 variants oculars I, V, IV insert. This is way ahead of that known from any other locality and 

 is directly comparable to the progressive variants of Strongylocentrotus purpuratus from Cali- 

 fornia, which in this respect is the most progressive species of the genus. The aberrant variants 



